The present invention relates to a method of providing an ink jet printing head with piezo-crystals which control the release of ink. The jet printing head is of the type having a plate-shaped basic body that includes a plurality of ink-filled pressure chambers and ink channels which connect the pressure chambers with outlet openings and an ink supply chamber. The printing head further has a membrane plate which is firmly secured to the basic body and is actuated by piezo-crystals for reducing the volume of the pressure chambers. The piezo-crystals are arranged on the membrane plate above the pressure chambers.
In a prior art ink jet printing head, such as disclosed in German Pat. No. 2,164,614, liquid ink-filled chambers are covered by individual membranes composed of thin metal plates. Individual piezo-electric crystals configured as electromechanical transducer devices are fastened to these metal plates. Such a printing head, equipped with, for example, seven printing units, has many individual parts which must be installed in several process steps. This process requires a high degree of skill on the part of the operator performing the installation, particularly since the plates of piezo-electric material are very small and are easily damaged. Further, the fragile plates must be installed and aligned with great accuracy.
Some of the above-mentioned drawbacks are overcome by the device taught in German Pat. No. 2,256,667. This patent teaches the use of a membrane plate which is connected with a one-piece piezo-ceramic plate to cover all of the pressure chambers. The piezo-ceramic plate can be locally activated by electrodes disposed on its surface in the region of the individual pressure chambers to activate individual chambers. The piezo-ceramic plate is provided with raised portions equipped with individual electrodes in the region of each of the individual fluid chambers. The respective raised portions of the piezo-ceramic plate have planar dimensions which correspond to the dimensions of the pressure chambers disposed in a base plate underneath them. If these dimensions are reduced to thus increase the density of the ink channels or pressure chambers in the basic body, the oscillating behavior of the piezo-ceramic raised portions is greatly influenced when the electrode layers are contacted by means of electrical wires. This prior art piezo-ceramic plate is easily installed but its manufacture is very expensive. Further, since the individual piezo-crystals are all fixed to a common piezo-ceramic plate, a relatively high voltage is required for compressing the chambers.